Injectable forms of purified atelopeptide collagen have been commercially available for many years for soft tissue augmentation. Daniels et al., U.S. Pat. No. 3,949,073, initiated the development of these materials. They describe an injectable solution of atelopeptide which when injected forms a fibrillar collagen implant. Forms of this material are now commercially available from Collagen Corporation (Palo Alto, Calif.) under the trademark ZYDERM.RTM.. ZYDERM.RTM. collagen implant is prepackaged in a one cc syringe (Medical Molding Co. of America) fitted with a 30 gauge needle.
U.S. Pat. No. 4,488,911 assigned to Collagen Corporation describe a method for preparing purified atelopeptide collagen in solution (CIS). Native collagen, typically of bovine origin, is extracted from tissue in dilute aqueous acid and then digested with a protease such as pepsin, trypsin or PRONASE.RTM. to remove the telopeptides from the ends of the collagen molecules. Atelopeptide collagen fibers may be reconstituted from CIS by raising the pH of the solution.
U.S. Pat. No. 4,582,640, also assigned to Collagen Corporation, describes a crosslinked form of atelopeptide fibrillar collagen. An injectable suspension of this crosslinked material is available commercially from Collagen Corporation under the trademark ZYPLAST.RTM.. This product is prepackaged in a syringe in the same manner as the ZYDERM.RTM. product.
U.S. Pat. No. 4,642,117, also assigned to Collagen Corporation, describes a method for reducing the viscosity of reconstituted CIS by passing the reconstituted fibers through a fine mesh screen.
ZYDERM.RTM. and ZYPLAST.RTM. collagen implants have enjoyed great commercial success and are used to treat a large variety of soft tissue anomalies. However, physicians have found one type of skin contour, fine superficial facial lines, particularly those about the eyes, (i.e., crows' feet) difficult to treat with these products. Specifically, physicians questioned about such treatment indicated inter alia that (1) they had negative experiences in using prior products due to lumpiness or beading of the injectate, (2) the nature of the skin surrounding the eye increased the possibility of the injection causing trauma or bruising of the area and (3) the treatment required greater control or precision than that which is achievable with these prior products.
Applicants addressed these shortcomings and found that a greatly improved product for treating fine superficial facial lines was achievable through a combination of modifying both the syringe and the injectate.